To improve the cleaning effect of cleaning baths, the liquid in the bath is excited with ultrasound. So called rod transducers, which are either completely immersed or mounted with only the resonator portion extending into the bath, are used for ultrasonic excitation.
The ultrasonic rod transducer has a resonator, to which an ultrasonic head is affixed at least at one end and acts as a radiator. The head forms a housing in which a piezoelectric ultrasonic transducer is accommodated.
The electrical transducer consists of a number of piezoelectric ceramic wafers. The Curie temperature of the ceramic wafers is about 300° C. If the ceramic wafers are heated to this temperature or higher, the piezoelectric effect vanishes irreversibly.
If the piezoelectric transducers are intended to be used in permanent operation, a distinct safety margin away from the Curie temperature must be maintained. Usually, the temperature at the surface of the ceramic transducer must not exceed about 150° C. Thus, if the bath temperature is about 130° C. a permissible temperature overage of only 20° C. remains.
Piezoelectric transducers made of ceramic are highly efficient. Still, the supplied electrical energy is not completely converted to ultrasonic energy, but rather in part, also results in heating of the transducer. The ultrasonic energy to be generated with the transducer thus is limited by the overtemperature of the transducer.
In known devices, the piezoelectric transducer is cooled essentially only by the mechanically coupled resonator, which consists of titanium. Titanium is a poor conductor of heat. There is practically no other cooling, since by reason of ultrasonic technology the housing of the head is filled with air, which forms an extremely poor conductor of heat, so that the heat, in practical terms, is not removed through the wall of the housing.
Based on the foregoing, the need existed for a more efficient ultrasonic transducer that can generate greater ultrasonic energy.